The invention relates to a watertight sensing device, primarily a pressure-sensing device, which can be suspended into the filling material, particularly into liquids.
In order to guarantee a lasting seal for the connecting cable of pressure sensors of this kind, it is necessary to relieve the seal from the pull of the sensor.
In the past this problem has been solved by allowing the weight of the sensor to be received by a steel wire provided inside of the connecting cable. The steal wire is usually secured inside the sensing device by means of a pressure sleeve, which is supported by a retaining plate belonging to the sensing device.
The electrically insulated connecting cable in such sensors must be provided with a shield, which usually consists of copper mesh and which is positioned below the insulating material of the cable jacket. To equalize the potential differences the shield is connected both to the metal housing of the sensor and to the ground of the control box.
In relieving pull it is also known to suspend the sensor within the filling material by means of an additional steel thread guided outside of the cable.
The use of an additional steel wire solely for the purpose of relieving pull is expensive.
The invention is thus based on the problem of simplifying a sensing device of the type indicated in the preamble to claim 1, specifically a device for which the relief from pull does not involve a relief wire.
This problem is solved with the features and measures indicated in claim 1.
The basic idea of the invention is to use the cable, which has no shielding, for the additional purpose of relieving pull, but without placing a load on the electrical conductors of the cable, which is not permissible under guidelines of the VDE (Association of German Electricians).
More specifically, the solution according to the invention consists in removing the insulating material of the outer cable jacket at that end of the shielding jacket that projects into the housing, and in securing this end in a hole bored in the sensor seat, specifically by means of a sleeve to be inserted into the end of the shielding jacket. To create a connection that is resistant to pull, another feature of the invention provides that the seat is inwardly compressed in the area of the sleeve inserted into the boring, a measure that reduces the cross-section and secures the shielding jacket.
With this kind of connection a secure electrical connection between the shielding and the sensor housing is assured; at the same time, the shielding itself serves to receive the pull of the sensor, and thus relieves the electrical conductors from pull.
According to claim 2, the seat will ideally exhibit a shoulder that narrows at the end protruding into the housing; with simple means and little force this shoulder can be pressed in a direction perpendicular to the center axis of the cable or sensor housing.
Another improvement in the attachment and the provision of electrical contacts is the subject matter of claim 3, according to which the outer rim of the sleeve, together with the end of the shielding jacket, is flanged in such a way that one face of the seat, specifically the shoulder of the seat, has a form-fitting, frictional connection.